At the present time, numerous industries in carrying out basic manufacturing steps, must perform processes of separation and recovery of substances. With the progress of technology increasing importance is given to the quality of the material which is used as an aid in processes of separation and recovery. The separating material quality should meet the requirements implicated in the solution of the following problems: (1) recovery of valuable substances; (2) regeneration of process water; (3) conditioning of process solutions and gases; (4) purification of effluents which is of prime importance for the environment protection.
It is known in the art to use naturally-occurring polymers as separation materials in the form of cotton and wool fabrics. At the present time there is a universal tendency to change cotton and wool filtering fabrics with filtration materials from synthetic polymeric fibres such as polypropylene, polytetrafluoroethylene and polyamide fibres.
The materials ensure only a mechanical separation of substances in accordance with the screening effect which does not enable differentiation of substances according to their type and properties.
The depth and selectivity of separation are substantially increased in the case where the filtration process is combined with back osmosis or ultrafiltration. Special membrane partitions are intentionally made for this purpose. The most extensively used are acetylcellulose membranes which are prepared by wet coagulation of a solution of acetylcellulose in formamide (cf. U.S. Pat. No. 3,666,508 Cl. 106-183).
A disadvantage of acetylcellulose filtering aids is their chemical instability; they feature low performance properties, limited service life and low resistance in acidic media.
To overcome the above-mentioned disadvantages and increase resistance to aggressive media, the company "Millipore Inc." his suggested production of membrane filters based on polytetrafluoroethylene or polyvinylchloride. However, these filtering materials at a high chemical resistance have hydrophobic characteristics. Therefore, they cannot be employed in processes of filtration of aqueous solutions.
The company "Akzona Inc." has developed a novel method for the preparation of microporous polymers based on polyolefins (cf. U.S. Pat. No. 4,247,498 Cl. 264-41). This method comprises dissolution of polyolefins at an elevated temperature in aromatic hydrocarbons, amines, alcohols or ketones, followed by cooling the heated solutions. The thus-prepared materials comprise, according to the company's contention, a new generation of porous materials with the brand name "Accurel" and a controlled pore diameter of 0.2 to 0.4 .mu.m.
At the present time the state of the art lacks a polymeric filtering material possessing required properties to satisfy modern requirements of substance purification, such as separation, recovery, removal, versatility in this particular area of application, and be simultaneously selective and efficient.
It is an object of the present invention to provide such a polymeric filtering material having a broad range of its filtering capacity, and which would be suitable for various processes of physico-chemical separation of substances and possess a high separation efficiency, stability in operation and simplicity in manufacture.